NiMH charger question

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zbaird
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Posted by zbaird: Fri. Sep 13, 2013 - 10:56 PM
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I have been given the remains of a toy R/C airplane which runs (ran) on NiMH batteries. It gets recharged in the field for a few minutes from a battery pack, then supposedly flies for a minute or so on a charge. Rinse and repeat.

It's no longer an airplane, just a pile o' parts. If I replace the rechargeable NiMH pack with standard alkalines, then don't even think about putting the charge voltage on it, are there likely to be problems?

Comments welcome and appreciated. A diode in there, perhaps, to make sure it is isolated from the charger circuit? Many thanks.

Chuck Baird

"I wish I were dumber so I could be more certain about my opinions. It looks fun." -- Scott Adams

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Plons
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Posted by Plons: Fri. Sep 13, 2013 - 11:13 PM
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Alkalines are not very good at high discharge currents. But it doesn't hurt to try.

IMO, replacing the NiMH-pack is the easiest and best solution.

You could also replace the pack with LiPo cells, but then it becomes tricky: charging of LiPo cells in series (what voltage has the current pack ?) requires a balancing circuit and a proper charger. Then there must be a discharge protection as well which prevents that individual cells go lower than 2.8V. And if LiPo's aren't treated with care, their revenge is that they catch fire.

Do you plan to play with this plane yourself, or is it for a grandchild ?

Nard

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zbaird
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Posted by zbaird: Fri. Sep 13, 2013 - 11:22 PM
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4 cells, at 1.2 v(?). They're the 1/4 AAA cells.

The plane is toast. What I have is the transmitter, the receiver/charger pcb, and a couple of motors with props. I grabbed the parts as they were headed for the trash for the transmitter and receiver since I hoard anything that looks like it might someday be useful to somebody on the planet. Anyone else (my wife leads the pack) would call it junk.

So no particular plans. I'll have to price 4 cell NiMH packs and see if I want to do the smart thing. There are a couple of chips (one potted, the other labelled "superchip" which is sort of cute) so figuring out which section is the charging circuit and removing it is probably beyond my capabilities.

My next plane (first plane, too) will be a quad copter. I blame toalan, Cliff, and DocJC for that desire.

I actually found some information on the "superchip," or at least its cousin. It's a generic remote control vehicle chip of some sort. My Chinese is a bit rusty.

Chuck Baird

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clawson
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Posted by clawson: Sat. Sep 14, 2013 - 11:14 AM
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Chuck,

Alkalines have far too high an internal resistance so cannot deliver the kind of current r/c motors typically take.

If a battery pack runs a plane for 6 minutes (say) it is discharging at 10C. So say you have a pack with a 500mAh capacity then at 1C it delivers 0.5A for one hour. At 5C it delivers 2.5A for 12 minutes. At 10C it delivers 5A for 6 minutes and at 20C it delivers 10A for 3 minutes.

NiCd often run at 10-20C. NiMh at 5-10C and modern LiPo can do 25-40C.

Alkaline cells are lucky if they can deliver 0.5-1C. They cannot deliver the demands of r/c flight.

Your best bet is to get replacement NiCd or NiMh packs from www.hobbyking.com. If feeling really adventurous get LiPo instead as they have a far higher energy density so you can carry the same amount of power as used previously in far less weight which can turn a lethargic r/c plane into an aerobat. (replacing brushed motors with far more efficient brushless can also help but you also have to replace the ESC and also pick a matched prop).

BTW in another life I'm the author of this thread:

http://www.rcgroups.com/forums/s...

the plane is completely built and ready and batteries (460mAh 2S) are charged (four packs) but the rain and wind here are atrocious and preventing me having the maiden flight which I hope to video. For the time being I'm flying Reflex XTR on a laptop a lot to hone my r/c control skills. I would HIGHLY recommend anyone trying to "go it alone" learning to fly r/c to get a PC simulator - preferably one you can control with your own Tx (assuming it has a trainer port).

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Plons
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Posted by Plons: Sat. Sep 14, 2013 - 11:37 AM
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Quote:
4 cells, at 1.2 v(?). They're the 1/4 AAA cells.
So the total pack has the same content as one AAA battery ? That's tiny ...

If you replace the pack with 4 AAA alkalines you may end up with a too high voltage (6 to 6.2V). So a diode in series is a good idea. That will get you through the testphase of this valuable junk :)

OTOH, I don't think that such a small NiMH-pack is very expensive. Then the charger can be connected just as it used to be.

Quadcopter: they're fun, aren't they ? I am about to buy one too. A year ago my son got me a helicopter (2 ft) but crashed it onto a lamppost on it's virgin flight. Quite some damage and no spareparts.

cheers

Nard

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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DocJC
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Posted by DocJC: Sat. Sep 14, 2013 - 11:51 AM
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Quote:
My next plane (first plane, too) will be a quad copter. I blame toalan, Cliff, and DocJC for that desire.

I have several R/C Helicopters, but no quads (yet). There are some truly amazing videos of high performance quads on the web. I would love to see their control algorithms. Some of the flight control algorithms need a PhD in math to understand them. I'm more of a Bang-Bang controller myself, occasionally with a little hysteresis if I'm feeling adventurous.

BTW, Chuck, I'm trying to clean up my computer room, but I am finding it to be a very slow and painful process. I think I must have a "Hoarder's gene". It is difficult to trash old parts, boards, and prototypes.

My largest helicopter is permanently grounded. It spent a Winter lost outdoors when it got away from me and flew off down the street, over the neighbors house, and into some woods. I spent hours looking for it. The neighbor kid found it the following Spring when he was walking through the woods with this dog. I replaced part of the rotor head and the batteries, but the motor just doesn't generate the lift required any more. It is a nice looking paperweight. Guess I'll save it for parts...

JC

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clawson
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Posted by clawson: Sat. Sep 14, 2013 - 01:35 PM
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I once had a plane "fly away". It remained lost for a few weeks. So I then strapped a small Aiptek camera to another plane with a servo operating the shutter. I flew a photo reconnaissance mission taking aerial shots of the area where the first had gone down. I eventually found it, it had gone much further (about 1/4 mile) than I thought and where I'd been searching on foot. After a couple of weeks the motor body was showing rust spots but the rest of the electronics (about £100 worth) could be re-used.

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DocJC
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Posted by DocJC: Sat. Sep 14, 2013 - 02:46 PM
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Gotta love planes with cameras.

A couple of year ago some friends got me a large Styrofoam B-52 bomber plane with an electric motor and a small camera. Flt time is only about 5 mins between charges, and the kids use to race and catch it on its final approach to landing.

With a GPS module the size of one's thumbnail now available, coupled with a 2 or 3 transistor VHF transmitter, a very small, lightweight, "smart" tracking bug is now certainly doable. Get within 1/4 - 1/2 mile of the device and locate it to within a few feet.

I purchased a Basic 4 android package a few weeks ago when it was mentioned here. It ought to be possible to do the Google Map on the phone, fed Bluetoothed info from a small micro, which gets its data from a Ham HT. QED.

JC

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zbaird
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Posted by zbaird: Sat. Sep 14, 2013 - 05:04 PM
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OK, this didn't go quite as I expected. Thanks to a tip and discount from Nard (thank you) I have ordered this quad. It comes with the spare parts he suggested, but it starts out in the U.S. so I don't have to hassle with customs. I'll have it on Tuesday, and will probably be able to add to my junk parts on Wednesday.

This may put a halt to my messing around with my other parts, but you never know. Thanks all for your comments so far.

Chuck Baird

"I wish I were dumber so I could be more certain about my opinions. It looks fun." -- Scott Adams

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Plons
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Posted by Plons: Sat. Sep 14, 2013 - 05:26 PM
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Quote:
and will probably be able to add to my junk parts on Wednesday.
LOVL

I should have ordered with amazon.co.uk, but I tend to find those things out when I already ordered somewhere else, ... like Banggood in China.

Oh well. Just have to be patient then.

Nard

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

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DocJC
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Posted by DocJC: Sat. Sep 14, 2013 - 10:44 PM
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Oh man, an open blade design.

Would you like to borrow a hard hat while you are getting started?

Where was that recent link about the individual who died from a propeller vs head injury while flying his copter?

Lessons learned, Darwin awards, etc., etc.

JC

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zbaird
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Posted by zbaird: Sat. Sep 14, 2013 - 11:27 PM
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I wasn't planning on getting close enough to the thing while it's running to let that be a problem. I'm sure that other guy (RIP) wasn't, either.

Jay, in the event of my demise, I bequeath you the contents of my garage (the good stuff), minus the stuff in there that isn't mine (the wife & kid's junk).

Chuck Baird

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Torby
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Posted by Torby: Sun. Sep 15, 2013 - 01:00 AM
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Electric model airplanes were made possible by high rate and high capacity rechargeable cells. NIMH cells are pretty inexpensive at places like all-battery.com.

I figure if I ever get back into RC flying, that I'd go electric. No more of that nasty glo-fuel mess all over everything.

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clawson
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Posted by clawson: Sun. Sep 15, 2013 - 12:29 PM
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Quote:

I wasn't planning on getting close enough to the thing while it's running to let that be a problem. I'm sure that other guy (RIP) wasn't, either.
Which is kind of the issue. The problem with quads can be a question of orientation. At least the body is shaped but I'd paint one end a dramatic colour to aid in visual orientation. Otherwise you can make a control input to try and move the thing away from you and it ends up moving it even closer to you.

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JohanEkdahl
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Posted by JohanEkdahl: Sun. Sep 15, 2013 - 12:49 PM
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Quote:

the contents of my garage (the good stuff), minus the stuff in there that isn't mine (the wife & kid's junk).

You have a wife that isn't yours in the garage? :wink:

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Kartman
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Posted by Kartman: Sun. Sep 15, 2013 - 01:09 PM
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Johan, it's an American thing. Sometimes there's three wives. Belgians have been known to do similar things.

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valusoft
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Posted by valusoft: Sun. Sep 15, 2013 - 01:11 PM
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Obviously too much information...

Ross McKenzie ValuSoft Melbourne Australia

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zbaird
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Posted by zbaird: Wed. Sep 18, 2013 - 07:11 PM
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Well, the new beast arrived and is pretty intimidating (to me anyway, an absolute neophyte), although the badly translated Chinese instruction manual gives a little levity. I'm thinking of tethering the thing (taut vertical string from ground to high tree running through hole in midsection away from props) to practice my ups, downs, and rotations prior to letting it loose. I still need to check out the training sites Cliff mentioned.

And back to the original topic: it turns out the plane's pcb has no charger; the charger smarts were in the base unit which I hadn't opened up so the original problem never really existed. The board is fairly complex but most of it is the receiver. I had assumed part of it was the charger.

I pulled the computer off the pcb and did a little reverse engineering and now have a transmitter and receiver that can send/recv 5 bits, plus 2 small motor drivers on the receiver board. What to build...?

I haven't done any experiments yet to see how immune to noise they are, but my guess is not very.

Chuck Baird

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Plons
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Posted by Plons: Wed. Sep 18, 2013 - 08:42 PM
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Quote:
I pulled the computer off the pcb and did a little reverse engineering and now have a transmitter and receiver that can send/recv 5 bits, plus 2 small motor drivers on the receiver board. What to build...?
And now get that Linux running !

Nard :lol:

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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DocJC
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Posted by DocJC: Thu. Sep 19, 2013 - 04:03 AM
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Chuck, there are obviously lots of web sites with quad copter and auto-pilot info, but when you have some time to spare take a look at ThisSite .

Very impressive.

JC

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clawson
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Posted by clawson: Thu. Sep 19, 2013 - 09:34 AM
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Chuck,

I would highly, highly recommend a simulator. I googled a bit and there are solutions for simulating quads. I'd explore one of those.

A lot of people seem to recommend Phoenix for this.

(I've been thinking of buying it anyway for 3D foamies - I already have Reflex XTR but I want something that will work with my Spektrum DX6i or at least use a Tx very similar).

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Plons
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Posted by Plons: Wed. Oct 16, 2013 - 04:51 PM
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Finally the quad came in. After 10 seconds of carefull skidding over the carpet, I smelled magic smoke. Damn. One prop went full speed. Of course one of the driving fets had released its magic. I was quite disappointed.
Today I replaced the fet (SOT23) and a 0402 resistor. OMG, that *is* small !
After half an hour with magnifiers (yes, I need more than one :D ) I fixed it with a IRLML2502PbF as replacement. What a joy ! It works again !

Flying inside the house is challenging but OTOH it allows me to train myself in using small corrections and the reflex to cut the throttle when it goes bad.

It is fun !

How are you doing, Chuck ?

Cheers

Nard

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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zbaird
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Posted by zbaird: Wed. Oct 16, 2013 - 05:14 PM
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Mine has a sad story that I haven't gotten around to fixing yet. I set it on the kitchen island, weighted down its landing struts so it couldn't move, then played with the remote control to get an idea of exactly what was happening with each prop as I moved the joystick and punched the buttons. I also tried the camera in still and video modes. All was well.

Then I was going to do a simulator like Cliff suggested, but I got really interested in the camera. So I found some compatible plugs in the pile-o'-parts and made a little harness to go between the camera and the quad so I could monitor the data traffic. It's 4 wires, so the question is whether there's a wire for "take a video" and a wire for "take a snapshot" or whether they're doing something more sophisticated.

Plugged it all together, attached the battery, and the earth stopped moving. Totally dead in the water. Now whether I shorted together the ground and supply (which is my guess, blowing the regulator), or whether in all the handling I just fried it via static I don't know. Shortly thereafter, although unrelated, I had a round of fatigue and fever which distracted me, and I just haven't gotten back to it yet.

I'm pretty sure it will fly again, once I start poking around and find out which one of the little microscopic specks on the pcb is the one I need to replace. I was tempted to just order another and have some spare parts, but thought better of it.

Thanks for asking. Please post some video when you have tamed your beast.

Chuck Baird

"I wish I were dumber so I could be more certain about my opinions. It looks fun." -- Scott Adams

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